Nanomaterials in Biosolids Inhibit Nodulation, Shift Microbial Community Composition, and Result in Increased Metal Uptake Relative to Bulk/Dissolved Metals

Abstract

We examined the effects of amending soil with biosolids produced from a pilot-scale wastewater treatment plant containing a mixture of metal-based engineered nanomaterials (ENMs) on the growth of Medicago truncatula, its symbiosis with Sinorhizobium meliloti, and on soil microbial community structure. Treatments consisted of soils amended with biosolids generated with (1) Ag, ZnO, and TiO2 ENMs introduced into the influent wastewater (ENM biosolids), (2) AgNO3, Zn(SO4)2, and micron-sized TiO2 (dissolved/bulk metal biosolids) introduced into the influent wastewater stream, or (3) no metal added to influent wastewater (control). Soils were amended with biosolids to simulate 20 years of metal loading, which resulted in nominal metal concentrations of 1450, 100, and 2400 mg kg(-1) of Zn, Ag, and Ti, respectively, in the dissolved/bulk and ENM treatments. Tissue Zn concentrations were significantly higher in the plants grown in the ENM treatment (182 mg kg(-1)) compared to those from the bulk treatment (103 mg kg(-1)). Large reductions in nodulation frequency, plant growth, and significant shifts in soil microbial community composition were found for the ENM treatment compared to the bulk/dissolved metal treatment. These results suggest differences in metal bioavailability and toxicity between ENMs and bulk/dissolved metals at concentrations relevant to regulatory limits.

Effects of silver sulfide nanomaterials on mycorrhizal colonization of tomato plants and soil microbial communities in biosolid-amended soil

“…The results reported here add clarification to a recent study by Judy et al (2015) which reported that PLFA biomarkers associated with AMF were significantly reduced and soil microbial communities significantly affected in biosolids-amended soils spiked with ENMs relative to biosolids-amended soils treated with bulk/dissolved metal . In that study, wastewater treatment plant influent was spiked with either Ag, TiO 2 , and ZnO ENMs, spiked with Ag, TiO 2 , and ZnO bulk/dissolved metal, or unamended with metals (control).…”

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects—An updated review

“…Considering that non‐labile transformation end products such as AgCl and Ag 2 S are expected to be stable in the environment and to have relatively low bioavailability (Lombi et al ; Donner et al ; Doolette et al , ), the risk to terrestrial ecosystems posed by Ag NMs would appear to be low, although uncertainties related to longer‐term transformations, dosimetry, are also relevant. This conclusion has been further supported by soil‐based studies demonstrating that Ag 2 S NMs presented minimal hazard to plant–microorganism symbioses (Judy et al , ), crop plants (Doolette et al ; Wang et al ), soil microorganisms (Judy et al ; Doolette et al ; Moore et al ), and soil invertebrates (Starnes et al , ).…”

“…Judy et al () reported data from a study examining the effects of amending soil with biosolids containing either bulk/dissolved TiO 2 , Ag, and ZnO, nanoparticulate TiO 2 , Ag, and ZnO, or containing no added metals (Chen et al ; Judy et al ). These biosolids were generated using pilot WWTP facilities, and the metal input into the waste streams was subjected to chemical conditions similar to what they would experience in an actual WWTP facility.…”

Considerations of Environmentally Relevant Test Conditions for Improved Evaluation of Ecological Hazards of Engineered Nanomaterials

“…195, 205, 206 Studies at entire WWTP scales elucidate ENM fates during wastewater treatment, including significant association with biological treatment biomass 201, 207 that becomes biosolids. 76, 208 However, only 50% of biosolids produced in the U.S. are land-applied, and these biosolids are used on less than 1% of agricultural land in the U.S. (http://www.epa.gov/biosolids). Biosolids are land-applied even less in the European Union.…”